Many mobile handsets and other consumer electronic devices are currently operated using touch technology. The number of these devices is rapidly increasing.
The most common touch technologies are resistive touch and capacitive touch. The resistive touch screens are the most common and have lower price.
A prior art resistive touch screen is described in FIG. 1. The touch screen is composed of two layers of thin conductive film (ITO) that are overlaid on top of each other. The film is conductive but has resistance. The two layers are separated by non conductive material such as air. When pressed the top layer makes contact with the lower layer and allows conductivity between the two layers.
Each of the film sheets has two electrodes/conductive bars on its sides. One film has two electrodes on its X axis, denoted X+ and X− while the other film has electrodes on its Y axis, denoted Y+ and Y−. The two film layers may be mounted on a glass surface above a display or directly over a display or may be mounted over any other surface.
The touch screen is connected to an analog touch controller that connects to a touch digital analysis controller that may operate as a standalone device or may be embedded on a CPU firmware. A sample implementation of such a system based on a commercial analog touch controller, namely, Texas Instruments TSC2007, is presented in FIG. 2.
The analog touch controller can apply voltage gap between two of the electrodes and measure the voltage on a third electrode. The standard practice is to apply voltage to X+ and X− and measure voltage on Y+, and then apply voltage to Y+ and Y− and measure voltage on X+. It can be easily shown that when a single point of contact is made between the two layers and assuming the layers are uniform, the measured voltage on Y+ divided by the voltage gap on X+ and X− would be the relative offset on the X axis of the contact point. The same applies to the second measurement that represents the offset on the Y axis.
Standard analog touch controllers also offer the option to apply voltage between the Y+ and X− electrodes and measure the voltage on either the X+ or Y− electrodes. These two measurements are referred to as Z1 and Z2. FIG. 3 illustrates a prior art implementation of such a controller.
It can be shown that the resistance of the touch point can be derived from the measurements in at least three separate ways.Rtouch1=Rxplate*X*(Z2/Z1−1),  (1)Rtouch2=Rxplate*X*(1/Z1−1)−Ryplate*(1−Y),  (2)where X and Y are the normalized X and Y offsets as derived from the first two measurements, Z1 and Z2 are normalized Z1 and Z2 measurements and Rxplate and Ryplate are the fixed resistance of the X and Y layers of film, which can be measured on production line or be found as part of calibration process.
It should be noted that three other cross measurements that involve supply of voltage potential between one electrode located on one of the resistive layers to another located on the other layer (Y−, X−) (Y+, X+) (Y−, X+) can be used to derive Z1 and Z2 measurements that can be used to derive Rtouch, as defined above.
A standard resistive analog touch controller usually also includes a touch detection circuitry that is used to indicate to the system touch analysis controller that a touch event had occurred. The analysis controller would then instruct the analog controller to perform a set of measurements to obtain the X and Y location of the touch point and optionally also the relative touch pressure as indicated by the touch resistance. The procedure is illustrated in FIG. 3.
The standard resistive touch screen is used to detect single finger or stylus pressed or movements (gestures) on the display surface. The technology was not designed to process more than a single point of connection on the display.
Newer technologies such as the capacitive touch screens and some more advanced variations on the resistive displays allow for detection of multiple simultaneous touch events on the display surface. Many of these solutions are composed of surfaces that are segmented to multiple separate regions. The controllers used to process the touch information are then connected via separate leads to each of these separate regions of the surface and apply multiple separate measurements to the resistance or capacitance of the plurality of regions. These solutions are more complex and higher cost in comparison to the standard resistive touch screen.
The most common usage for the multi touch technology is for detection of complex gestures that involve more than one finger touching the display. Many of these gestures are based on two finger operation. Some examples include double finger swiping of the fingers across the display (horizontally or vertically), double finger tap on the display, and pinch movement of two fingers.
In order to allow for lower cost design it would be beneficial to be able to support the detection of these most common double finger gestures and distinguishing them from single finger gestures using simpler lower cost technology. The present invention satisfies this need.